CN1630283A - Method of transmitting preamble for synchronization in a MIMO-OFDM system - Google Patents

Abstract

A method and apparatus for transmitting a preamble for frame synchronization and channel estimation in a MIMO-OFDM communication system are provided. An OFDM communication system using Q transmit antennas generates a base preamble sequence including a CP and an orthogonal sequence. If Q a predetermined number M, a preamble sequence for a kth antenna is S(t-(k-1)T/Q). If Q > M and k M, the preamble sequence transmitted for the kth antenna is S(t-(k-1)T/Q). If Q > M and k > M, the preamble sequence for the kth antenna is (-1) (PS-1) S(t-(k-1)T/Q). Here, S(t) is the orthogonal sequence, T is the period of the orthogonal sequence, and PS is an index indicating a transmission period of the preamble sequence. The preamble sequences are at least twice transmitted from the Q transmit antennas.

Description

In multi-input multi-output-orthogonal frequency-division multiplexing system for launching synchronously leading method

Technical field

The present invention relates generally to a kind of multi-I/O OFDM (MIMO-OFDM) communication system, especially relates to a kind of leading method and apparatus of launching in order to reach frame synchronization.

Background technology

Because OFDM shirtsleeve operation, the robustness of anti-multichannel decline, can be called the ability that improves data rate on the frequency of subcarrier by the parallel transmission data-signal with it, OFDM is thought a kind of basic transmission plan in the next generation wireless communication widely.For fear of the interference of adjacent carrier, mutually orthogonal between the subcarrier.Their frequency spectrum overlaid so that subcarrier be separated from each other with very little gap.

Ofdm system is offset for sum of errors, comprises frequency deviation, and frame or intersymbol timing error and because that the high ratio (PAPR) of peak-to-average power ratio causes is non-linear are highstrung.Many ofdm systems adopt coherent detection rather than difference modulation and demodulation in order to obtain the additional signal to noise ratio (snr) gain of about 3dB.The depending on channel condition information (CSI) and whether can obtain of the quite big degree of their performance.

The use of many transmit/receive antennas has further improved the communication quality and the throughput of ofdm system.This ofdm system is called as the MIMO-OFDM system, and this system is different from the single output of single input (SISO)-ofdm system.

Data can be transmitted simultaneously in spatial domain in the MIMO-OFDM system on a plurality of subchannels, and no matter whether transmitter needs CSI.Subchannel is meant from a plurality of transmitting antennas to the wireless path a plurality of reception antennas.Therefore, the MIMO-OFDM system provides the data rate higher than SISO-OFDM system.

Typically, the MIMI/SISO-OFDM system need be in the frame synchronization on time and the frequency, and channel parameter estimation and noise change.For synchronous and estimation, adopted targeting sequencing (just, training symbol or training sequence).

Fig. 1 shows the OFDM frame structure that comprises targeting sequencing in typical ofdm communication system.With reference to figure 1, targeting sequencing is made of the special symbol that the prefix as the OFDM frame adds.In general, leading structure between transmitter and receiver and content are known.It is in order to have relative low complexity and performance to greatest extent to be provided synchronously with in the estimation procedure that leading quilt so constitutes.

Desirable preamble structure satisfies following demand:

(1) for regularly synchronously fabulous compensatory;

(2) for the low PAPR of high power transmission;

(3) for the feasibility of channel estimating;

(4) for the feasibility of the frequency offset estimating on wide region; With

(5) low computation complexity, low consumption and pinpoint accuracy.

To the traditional preamble structure that be used for MIMO-OFDM frame synchronization and channel estimating be described below.

First the known leading emission/reception programme that is used for MIMO-OFDM frame synchronization is by the identical information sequence of all transmission antennas transmit.

The MIMO-OFDM system must have fabulous characteristic from the cross correlation of the autocorrelation in time domain cycle of the sequence of different transmission antennas transmit and sequence.Desirable auto-correlation and their cross correlation are determined by equation (1) and equation (2) respectively:

Wherein subscript * represents adjoint operator, and N represents sequence length, the sequence number of q and q ' expression transmitting antenna, s _{Q, n}Expression is a n data symbol the sequence of N from the length of q transmission antennas transmit.The sequence that satisfies equation (1) is an orthogonal sequence.At this, subscript N represents sequence period.

Under perfect condition, matrix is a cell matrix during from the sequence of N transmission antennas transmit empty.Yet this is impossible in it is used because the number of transmitting antenna must with the equal in length of sequence.

In first leading emission/reception programme, designated the duplicating by the predetermined orthogonal sequence that appointment is used for first antenna of targeting sequencing is applied to other antenna, reaches frame synchronization, and is represented as

s _{Q, n}=s _nTo whole q

.....(3)

A significant disadvantages of such scheme is that SNR can be very low under the situation of correlated channels.For example, 2 * 2MIMO system that adopts two transmitting antennas and two reception antennas, received signal is expressed as

$r_j[n,k]=\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{ij}}[n,k]S[n,k]+n_j[n,k]---\left(4\right)$

R wherein _j[n, k] is illustrated in the frequency-region signal that j antenna receives, n _j[n, k] represents white Gauss noise, and Hij represents the channel response from i transmitting antenna to j reception antenna, S[n, k] expression is arranged in n symbol of k subcarrier.As in equation (4), if H _1jBe approximately equal to-H _2j, the SNR of the signal that receives so can be very low.

The traditional leading emission/reception programme of another of MIMO-OFDM frame synchronization has adopted the quadrature complex phase bit sequence of direct modulation.

Directly modulation orthogonal complex phase bit sequence is a sequence that is used to constitute the chirp type of targeting sequencing.If P is a prime number, so directly modulation orthogonal complex phase bit sequence is made of (P-1) individual orthogonal sequence.Its optimum their cross correlation is expressed as

According to second kind of leading emission/reception programme, transmission antennas transmit has the identical targeting sequencing of (P-1) individual orthogonal sequence.There is following point in this scheme:

(1) though directly the length of modulation orthogonal complex phase bit sequence be prime number square, in general the length of an OFDM frame must be 2 powers, for example, 64,128,256 ...; With

(2) when must be when each point all will obtain a desirable frame, the complexity that reduces required multiplying be impossible, the therefore a large amount of calculating of needs.

Now, the known leading emission/reception programme that is used for the MIMO-OFDM channel estimating will be introduced below.

The monadic symbols optimum training technology that the first kind of leading emission/reception programme that is used for the MIMO-OFDM channel estimating is Geoffrey Li.Fig. 2 illustrates the preamble structure that a basis is used for first kind of leading emission/reception programme of MIMO-OFDM channel estimating.

With reference to figure 2, Q transmitting antenna is shown, first antenna emission targeting sequencing S (t), all the other each antenna emission targeting sequencing S (t-T/Q) ..., or S{t-(Q-1) T/Q}, these sequences are by changeing the symbol of predetermined number to the targeting sequencing wheel of the antenna of front, i.e. T/Q symbol and obtaining.Q=Floor (N/L ₀), wherein, N is the number of subcarrier, L ₀Maximum time delay expansion for subchannel.Floor () is for obtaining the power function of integer, and T is the cycle of targeting sequencing.T is the number of symbols that is contained in the targeting sequencing, N, and symbol period T _sProduct.

Received signal on j reception antenna by

$r_j[n,k]=\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{ij}}[n,k]S[n,k]W_N^{k\·L_0}+n_j[n,k]---\left(6\right)$

Determine, wherein W _NExpression N point fast Fourier conversion (FFT).As p[n, k]=r[n, k] * S ^*[n, k], equation (6) is expressed as

$P_j[n,k]=\underset{i}{\mathrm{\Σ}}{H}_{\mathrm{ij}}[n,k]W_N^{-k\·L_0}+n_j[n,k]\·S^{*}[n,k]---\left(7\right)$

Fig. 3 shows P _jAn example of the time domain channel response characteristic of [n, k].With reference to figure 3, h _0jBe channel response characteristic from first transmitting antenna to receiver, h _1jBe channel response characteristic from second transmitting antenna to receiver, h _2jBe channel response characteristic from the 3rd transmitting antenna to receiver, h _3jIt is channel response characteristic from the 4th transmitting antenna to receiver.From the targeting sequencing of transmission antennas transmit by having the channel of different qualities.The time domain size T/Q of channel changes along with the number Q of transmitting antenna.

Mean square error (MSE) in the monadic symbols optimal sequence technology is passed through

$\mathrm{MSE}=\frac{L_0}{N}\·{\mathrm{\σ}}_n^2---\left(8\right)$

Calculate, wherein, σ _N.-σ _nThe expression noise power.

According to the first kind of leading emission/reception programme that is used for the MIMO-OFDM channel estimating,, only there is a training sequence structure to satisfy the demand though targeting sequencing can transmit on all subcarriers.Yet because each transmitting antenna training sequence is taken turns the symbol that has changeed predetermined number, the number of transmitting antenna is subjected to taking turns the restriction of the length of the number of symbol of commentaries on classics and training sequence.

The second kind of leading emission/reception programme that is used for the MIMO-OFDM channel estimating adopts the Space Time Coding of CordonL.Stuber and Apurva N.Mody.In this scheme, known symbol in spatial domain according to time and space, just according to transmitting antenna, by invert and conjugation launched by quadrature.Be used to adopt two transmitting antennas and two reception antennas 2 * 2 systems a targeting sequencing by

$\left[\begin{array}{cc}{S}_1& S_2\\ {-\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="A20041001047300171.png,A20041001047300271.png"\; state="\{\{state\}\}">S</figure-callout>}}_2^{*}& S_1^{*}\end{array}\right]---\left(9\right)$

Constitute.

Above-mentioned matrix means symbol S ₁And S ₂Launched symbol-S2 continuously from first transmitting antenna ^*And S1 ^*Launched continuously from second transmitting antenna.

For one 4 * 4 system, targeting sequencing can by

$\left[\begin{array}{cccc}{S}_1& S_1& S_1& S_1\\ {-S}_2& S_1& {-S}_4& S_3\\ {-S}_3& S_4& S_1& {-S}_2\\ {-S}_4& {-S}_3& S_2& S_1\end{array}\right]---\left(10\right)$

Constitute.

Fig. 4 shows the emission/reception according to a targeting sequencing of second kind of leading emission/reception programme in the MIMO-OFDM channel estimating.

With reference to figure 4, Q targeting sequencing, each contains Q symbol, and is provided for Q transmitting antenna to time t+ (Q-1) Ts by Q OFDM modulator from time t.The Ts is-symbol cycle.Targeting sequencing is by having channel response characteristic h ₁₁To h _QLQ * L subchannel arrive L reception antenna.L ofdm demodulator assembled the signal R1 that receives at L reception antenna from time t to time t+ (T-1) Ts to R _QL, set up a Q * L received signal matrix.

In second kind of leading emission/reception programme, the minimal amount of the training symbol that each transmitting antenna needs equals the number of transmitting antenna.Along with increasing of the training symbol that uses, it is longer that targeting sequencing becomes.This is infeasible for communication burst or high mobility.

Summary of the invention

An object of the present invention is for the advantage below solving the problems referred to above and/or shortcoming at least fully and providing at least.Therefore, an object of the present invention is in the MIMO-OFDM system, to provide an effective targeting sequencing structure and a kind of effective targeting sequencing launching technique.

Another object of the present invention is to be used for providing in the MIMO-OFDM system a kind of leading method and apparatus that is used to generate many symbols structure when empty.

In the MIMO-OFDM communication system, above-mentioned purpose realizes by launching leading method and apparatus for frame synchronization and channel estimating.Adopt the ofdm communication system of Q transmitting antenna to produce base preamble that comprises Cyclic Prefix and orthogonal sequence of generation; With the symbol that passes through this orthogonal sequence wheel is changeed predetermined number, be the targeting sequencing of each generation in Q the transmitting antenna, and from Q the targeting sequencing at least twice that transmission antennas transmit generated.

If Q≤one is a predetermined number M, the targeting sequencing of k antenna is S (t-(k-1) T/Q).If Q＞M and k≤M, the targeting sequencing that k antenna launched is S (t-(k-1) T/Q).If Q＞M and k＞M are (1) to the targeting sequencing of k antenna ^(PS-1)S (t-(k-1) T/Q).Wherein, S (t) is an orthogonal sequence, and T is the cycle of this orthogonal sequence, and PS is the index in the emission cycle of indication targeting sequencing.

Description of drawings

Above-mentioned and other purposes of the present invention, feature and advantage will become more apparent by the detailed description below in conjunction with accompanying drawing, wherein:

Fig. 1 shows a kind of structure that includes the OFDM frame of targeting sequencing in a typical ofdm communication system;

Fig. 2 shows the preamble structure according to a kind of traditional leading emission/reception programme that is used for the MIMO-OFDM channel estimating;

Fig. 3 shows P _jThe example of the time domain channel response feature of [n, k];

Fig. 4 shows the emission/reception according to the targeting sequencing of another the traditional leading emission/reception programme that is used for the MIMO-OFDM channel estimating;

Fig. 5 is the simplified block diagram of typical mimo system;

Fig. 6 is the block diagram of the transmitter in the application MIMO-OFDM of the present invention system;

Fig. 7 is the block diagram of the receiver in the application MIMO-OFDM of the present invention system;

Fig. 8 shows an embodiment according to preamble structure of the present invention;

Fig. 9 shows the leading emission shown in Fig. 8;

Figure 10 shows the result according to frame synchronization of the present invention;

Figure 11 shows the embodiment that is used for the preamble structure of 4 * 4MIMO system according to the present invention;

Figure 12 shows the embodiment that is used for the preamble structure of 6 * 6MIMO system according to the present invention;

Figure 13 shows leading in the matrix-block shown in Figure 12; With

Figure 14 is a chart, shows in adopting multichannel WLAN (wireless local access network) system of preamble structure of the present invention channel estimation gains about MSE.

Embodiment

Below with reference to the accompanying drawings the preferred embodiments of the present invention are described.In the following description, known function and structure will not be described in detail, because they may make the present invention unclear on unnecessary details.

Application MIMO-OFDM of the present invention system is at first described below.

Fig. 5 is the simplified block diagram of a typical mimo system.With reference to figure 5, Q * L subchannel 30 is defined as between transmitter 10 with Q transmitting antenna and receiver 20 with L reception antenna.In the subchannel 30 each has unique channel response characteristic h _Ql, these characteristics are expressed as the channel matrix H of a Q * L _QL

Fig. 6 is the block diagram of the transmitter in the application MIMO-OFDM of the present invention system.Transmitter gains to obtain antenna diversity by the identical user profile of a plurality of transmission antennas transmit.

With reference to figure 6, encoder (ENC) 102 produces a coded sequence by adopting predetermined sign indicating number speed to encode to information sequence S (t).Demodulation multiplexer (DEMUX) 104 will arrive on a plurality of interleavers (INT) 106 to 114 corresponding to transmitting antenna 112 to 120 through the sequence allocation of coding.Each of interleaver 106 to 114 interweaves to input bit.Each mapper (MAP) 108 to 116 is according to mapping ruler, and for example PSK (phase shift keying) or QAM (quadrature amplitude modulation) are mapped to modulation symbol with interleaving bits.

In the OFDM modulator (MOD) 110 to 118 each produces an OFDM symbol by insert a frequency pilot sign between the modulation symbol of each predetermined number, add targeting sequencing by beginning and produce an OFDM frame, and the OFDM frame is carried out inverse FFT (IFFT) with known symbol at the OFDM of predetermined number symbol.IFFT OFDM frame is launched to 120 by their corresponding transmitting antennas 112 by RF (radio frequency) module (not shown).

Fig. 7 is the block diagram of the receiver in the application MIMO-OFDM of the present invention system.Transmitter shown in this receiver and Fig. 6 is complementary.

With reference to figure 7, the signal that receives on reception antenna 202 to 216 is imported into the input of ofdm demodulator (DEMOD) 204 to 218 by a RF module (not shown).Each of ofdm demodulator 204 to 218 is told leading on basis frame by frame from the OFDM sign field, by detecting leading accurate acquisition frame synchronization, and produce a plurality of modulation symbols by signal is carried out fast Fourier transform.Though do not illustrate, the detected leading channel estimator that can be applicable to, this channel estimator are used to estimate the channel response characteristic from transmitted from transmitter to receiver.

Each of de-mapping device (DEMAP) 206 to 216 is separated mapping according to the mapping ruler of separating corresponding to the mapping ruler that is used for transmitter to the modulation symbol that receives.Each of deinterleaver (DEINT) 208 to 216 is carried out deinterleaving according to the bit of process being separated mapping corresponding to the deinterleaving rule of the interlacing rule that is used for transmitter.212 pairs of bits through deinterleaving of multiplexer (MUX) carry out multiplexed, and decoder 210 is by decoding recovering information sequence S (t) according to the sign indicating number speed that adopts at transmitter to the multiplexed bit of process.

In having the MIMO-OFDM system of above-mentioned structure, targeting sequencing is made of special symbol, and this special symbol generates and be attached to the beginning that the OFDM frame is indicated the OFDM frame by the OFDM modulator.Mobile radio station must receive these data synchronously with the starting point of data.For this reason, mobile radio station will obtain to be applied to usually the targeting sequencing of whole system before receiving data.

Targeting sequencing is used to frame synchronization, Frequency Synchronization (just, frequency offset estimating), and channel estimating.Ofdm communication system adopt the targeting sequencing be in each frame or data burst beginning come the estimated time/frequencies/channels information, and adopt be inserted into the Cyclic Prefix (CP) that solves intersymbol interference and be inserted into frequency pilot sign between the modulation symbol come to time/frequencies/channels information upgrades.

As is known, frame synchronization was undertaken by two stages: rough frame synchronization and accurate frame synchronization.

Rough frame synchronization is to detect the process of the starting point of OFDM frame by sampling in approximate scope.The correlation peak of CP is used for rough frame synchronization.Following equation is represented measuring of rough frame synchronization,

${\mathrm{\&phi;}}_n={\left|\right|\underset{k=0}{\overset{G-1}{\mathrm{\&Sigma;}}}(r_{j,n+k}^{*}\&CenterDot;r_{j,n+k+N})\left|\right|}^2---\left(11\right)$

Wherein G represents the size of the window of frame synchronization, r _{J, x}Be illustrated in x signal in the sequence that receives on j the reception antenna, N represents the length of sequence.Therefore, rough frame starting point is the timing index n of maximization Φ n.

Rough frame synchronization has been dwindled the scope of accurate frame synchronization.Equation (12) is compared computer capacity with equation (2) aspect the crossing dependency of accurate frame synchronization and is narrowed down calculating.

$\mathrm{\&phi;}\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{S}_{q,n}^{*}\&CenterDot;S_{q^{\&prime;},{(n+k)}_N}=0\mathrm{for\; all\; k}\&Element;K_{\mathrm{catch}},q\&NotEqual;q^{\&prime;}---\left(12\right)$

S wherein _{Q, n}N the data symbol of expression from the sequence of q transmission antennas transmit, K _CatchThe scope of representing accurate frame synchronization.Therefore, the frame starting point is to make the φ (k) that measures of accurate frame synchronization become 0 timing index k.

To introduce according to the present invention an embodiment of targeting sequencing structure specific in the multichannel wlan system below.

Allow a root mean square (RMS) postpone to equal 50ns, the sample time equals 25ns, and CP length equals 32 points, and the total length of data equals 128 points.The length of the valid data in data is 112 points, and DC (direct current) and the interior edge component of signal frequency band are zero.Here, 2 * 2 of two transmitting antennas of employing and two reception antennas mimo system is as an example.Point refers to submit to the position of the subcarrier of N-point FFT.For example, if CP be 32 long, this means that CP launches on 32 subcarriers.

At first, orthogonal sequence adopts CAZAC (the constant amplitude zero auto-correlation) sequence of an expansion to generate.

For example, a basic CAZAC sequence is

1，1，1，1，1，j，-1，-j，1，-1，1，-1，1，-j，-1，j

.....(13)

By in this basic CAZAC sequence, between every pair of adjacent element, inserting three zero, just can generate following sequences

1，0，0，0，1，0，0，0，1，0，0，0，1，0，0，0，1，0，0，0，j，0，0，0，-1，0，0，0，-j，0，0，0，1，0，0，0，-1，0，0，0，1，0，0，0，-1，0，0，0，1，0，0，0，-j，0，0，0，-1，0，0，0，j

.....(14)

The peak value of the CAZAC sequence of above-mentioned expansion and the ratio of average power are 6dB.

For frequency spectrum shaping, above-mentioned orthogonal sequence is switched to frequency domain.Resulting new sequence is switched to time domain once more, obtains targeting sequencing thus.

Thereby, draw according to leading structure of the present invention, shown in following table 1.

Table 1

????CP0	????S 64[1:64]	????S 64[1:64]	Antenna 0
				????CP1	????S 64[33:64] ????S 64[1:32]	????S 64[33:64] ????S 64[1:32]	Antenna 1

Fig. 8 shows the preamble structure according to one embodiment of the present of invention, and Fig. 9 shows emission leading shown in Fig. 8.Situation as described above, shown in preamble structure be used for 2 * 2 mimo system.

With reference to the sequence of figure 8, the first antennas (antenna 1) emissions 64 bits, S[1:64] be used for for the first emission cycle, the wheel that second antenna (antenna 2) is launched this sequence changes the form S[33:64 of 32 bits] S[1:32].32 bits are that sequence length 64 is launched the merchant that the number 2 of antenna removes.These sequences are repeated emission in the second emission cycle.The emission of 64 bit sequences is equivalent to adopt 64 subcarriers.Therefore, as shown in Figure 9, first antenna is launched list entries at subcarrier #0 to #63, and second antenna is launched list entries at subcarrier #32 to #31.

Then, receiver passes through the CAZAC sequence of expansion and the complex symbol crosscorrelation that receives thus

${\mathrm{\&Phi;}}_n=\underset{q=1}{\overset{Q}{\mathrm{\&Sigma;}}}\frac{{\left|{\mathrm{\&phi;}}_{q,n}\right|}^2}{{\left(P_n^{\&prime;}\right)}^2}$

Wherein ${\mathrm{\&phi;}}_{q,n}=\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}(S_{q,k}^{*}\&CenterDot;r_{j,n+k})$

Carry out accurate frame synchronization, wherein N is the length according to targeting sequencing of the present invention, and Q is the number of transmitting antenna, s _{Q, k}Be k symbol from the targeting sequencing of q transmission antennas transmit, r _{J, n+k}Be (n+k) the individual signal in the targeting sequencing that on j reception antenna, receives.

Similarly, the starting point of frame is confirmed as time point n, wherein Φ n=0.

Because time index is represented a FFT point in accurate frame synchronization, whole complex multiplication can increase sizable complexity.Yet along with the use according to the CAZAC sequence of simple structure of the present invention, only addition and conversion are just enough.

Because sequence of the present invention wheel changes, received signal by

r _j(k)＝H _0j(k)S(k)+H _1j(k)·(-1) ^kS(k)+n _j(k)

... .. (16) decides.

Even channel is relevant mutually, it also is impossible reducing SNR in system.Yet analog result has shown that it is stable that the present invention compares with traditional technology that identical sequence is applied to all antennas.

Figure 10 shows the result according to frame synchronization of the present invention.Temporal conversion in rough and accurate frame synchronization tolerance is illustrated.In Figure 10, the time point with correlator peak values is very tangible in accurate frame synchronization.

Yet, according to embodiments of the invention as shown in Figure 8, the identical targeting sequencing of each transmission antennas transmit in two emission cycles, it can also further be designed to another one embodiment, this embodiment is the identical sequence of each transmission antennas transmit in more than two emission cycles, to realize more stable frame synchronization and more precise channels estimation.

Figure 11 shows the embodiment that is used for the preamble structure of 4 * 4 mimo system according to of the present invention.

With reference to Figure 11, in first emission cycle, the CAZAC sequence S (t) of an expansion of first antenna (antenna 0) emission, the wheel of second antenna (antenna 1) emission S (t) changes the form of T/4 symbol, S (t-T/4).T represents sequence period.In an identical manner, third and fourth antenna (antenna 2 and antenna 3) is launched T/2 the symbol of wheel commentaries on classics of S (t) and the form that wheel changes 3T/4 symbol, S (t-T/2) and S (t-3T/4) respectively.Each transmitting antenna is second or the identical sequence of more a plurality of emission cycle repeat its transmission.

In general, the preamble structure that is used for Q transmitting antenna that draws is as shown in table 2.In table 2, PS represents the index in the emission cycle of targeting sequencing.

Table 2

?????PS	????1	????2	...
				Antenna 1	????S(t)	????S(t)	...
Antenna 2	????S(t-T/Q)	????S(t-T/Q)	...
				????...	????...	????...	...
Antenna k	????S(t-(k-1)T/Q)	????S(t-(k-1)T/Q)	...
				????...	????...	????...	...
Antenna Q	????S(t-(Q-1)T/Q)	????S(t-(Q-1)T/Q)	...

Simultaneously, if Q greater than predetermined number M, (M+1) individual antenna is launched circularly to a last antenna and is assigned to the sequence of first antenna to M antenna.Preamble structure constitutes by repeating to be assigned to first those sequences to M antenna in spatial domain.

CP length is decided by the scope of frame synchronization.Therefore, the maximum available number M of transmitting antenna is floor (N/L ₀).L ₀Maximum time delay expansion for subchannel.If Q is greater than M, preamble structure constitutes by repeating to be assigned to first those sequences to M antenna in spatial domain, and (M+1) individual emission circularly to a last antenna is assigned to first sequence to M antenna.Simultaneously, in order to ensure stable channel estimating, preamble structure is set quadrature in time domain.

For example, if M=4, Q=6, the preamble structure that obtains is as shown in table 3.

Table 3

????PS	????1	????2	????3	...
					Antenna 1	????S(t)	????S(t)	????S(t)	...
Antenna 2	????S(t-T/4)	????S(t-T/4)	????S(t-T/4)	...
					Antenna 3	????S(t-T/2)	????S(t-T/2)	????S(t-T/2)	...
Antenna 4	????S(t-3T/4)	????S(t-3T/4)	????S(t-3T/4)	...
					Antenna 5	????S(t)	????-S(t)	????S(t)	...
Antenna 6	????S(t-T/4)	????-S(t-T/4)	????S(t-T/4)	...

Figure 12 shows the preamble structure that is used for 6 * 6 mimo system according to one embodiment of the present of invention.

With reference to Figure 12, in the first emission cycle, first antenna (antenna 0) emission expansion CAZAC sequence S (t).The second, the third and fourth antenna (antenna 1, antenna 2 and antenna 3) is launched respectively by S (t) is taken turns respectively changes T/4, S (t-T/4), S (t-T/2) and S (t-3T/4) that T/2 and 3T/4 produce.The the 5th and the 6th antenna (antenna 4 and antenna 5) is transmitting sequence S (t) and S (t-T/4) respectively, once more from S (t).Except the 5th and the 6th antenna in order to guarantee in the orthogonality of time domain and the second and the 4th emission cycle launch respectively counter-rotating sequence-S (t) and-S (t-T/4), in the second, the third and fourth emission cycle, each antenna is the identical sequence of repeat its transmission all.

In these cases, matrix-block Guarantee the orthogonality of time domain.The line display of matrix-block respectively contains the antenna sets of M transmitting antenna, and sequence period is shown in tabulation.Therefore, for M=4, an elements A can be supplied with nearly four antennas.When M=4, this preamble structure can be supported nearly eight transmitting antennas.

Figure 13 shows in matrix-block as shown in figure 12 leading.With reference to Figure 13, the elements A of matrix-block that is used for one 6 * 6 mimo system is

$\left[\begin{array}{c}S\left(t\right)\\ S(t-T/M)\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ S(t-(M-1)T/M)\end{array}\right].$

Each antenna time domain repeat element A or-the corresponding row of A.In this case, although increased complexity, the accuracy of frame synchronization and channel estimating has all improved.

In general, and a given Q transmitting antenna (Q＞M), the different targeting sequencing of antenna emission in the different antennae group.Have first in first antenna sets of M antenna k antenna (the emission targeting sequencing S (t-(k-1) T/Q) of k≤M), and have (M+1) individual in second antenna sets of a last antenna the individual antenna of k ' (k '＞M) emission targeting sequencing (1) ^(PS-1)S (t-(k-1) T/Q).At two or more each antennas of emission cycle identical targeting sequencing of repeat its transmission all.

Figure 14 is a curve chart, shows the channel estimation gains about the MSE in the multichannel wlan system that adopts targeting sequencing of the present invention.* be illustrated in traditional preamble structure and the corresponding MSE of SNR ,+be illustrated in the preamble structure of the present invention and the corresponding MSE of SNR.As can be seen from Figure 14, preamble structure of the present invention all provides less MSE on all SNR.

As mentioned above, preamble structure of the present invention is controlled leading length neatly.Therefore, be feasible for what happen suddenly with communicating by letter of high mobility.Simultaneously, the circulation of sequence brings very high performance frame synchronization and clock skew synchronous in the time domain.

Though the present invention reference some preferred embodiment wherein is illustrated and describes, but to those of ordinary skill in the art, can understand under the situation that does not break away from the spirit and scope of the invention, can do various changes in form and details, as defined in the appended claims.

Claims (12)

1, a kind ofly in adopting the orthogonal FDM communication system of Q transmitting antenna, launch leading method, may further comprise the steps:

(1) generates a base preamble that comprises Cyclic Prefix (CP) and orthogonal sequence; With

(2) by this orthogonal sequence wheel being changeed the symbol of predetermined number, be the targeting sequencing of each generation in Q the transmitting antenna, and from Q the targeting sequencing at least twice that transmission antennas transmit generated.

2, the method for claim 1, wherein step (2) comprises such step, if Q is less than or equal to predetermined number M, generate a targeting sequencing for each transmitting antenna so, to such an extent as to from the targeting sequencing of k antenna emission is S (t-(k-1) T/Q), wherein S (t) is an orthogonal sequence, and T is the cycle of this orthogonal sequence.

3, the method for claim 1, wherein step (2) comprises such step, if Q is greater than M, generate a targeting sequencing for each transmitting antenna so, to such an extent as to if k is less than or equal to M, targeting sequencing from the emission of k antenna is S (t-(k-1) T/Q) so, and if k greater than M, the targeting sequencing of launching from k antenna is (1) so ^(PS-1)S (t-(k-1) T/Q), wherein S (t) is an orthogonal sequence, T is the cycle of this orthogonal sequence, and PS is the index in the emission cycle of indication targeting sequencing.

4, method as claimed in claim 2, wherein M is with the length N of the targeting sequencing maximum delay spread L divided by subchannel ₀The merchant's of gained integer part.

5, method as claimed in claim 3, wherein M is with the length N of the targeting sequencing maximum delay spread L divided by subchannel ₀The merchant's of gained integer part.

6, method as claimed in claim 2, wherein M is 4.

7, method as claimed in claim 3, wherein M is 4.

8, the method for claim 1, wherein orthogonal sequence is CAZAC (the constant amplitude zero auto-correlation) sequence of an expansion.

9, method as claimed in claim 8, wherein the CAZAC sequence of this expansion is 1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0, j, 0,0,0 ,-1,0,0,0 ,-j, 0,0,0,1,0,0,0 ,-1,0,0,0,1,0,0,0 ,-1,0,0,0,1,0,0,0 ,-j, 0,0,0 ,-1,0,0,0, j.

10, a kind of in adopting the orthogonal FDM communication system of two transmitting antennas the leading method of emission, comprise the following steps:

Generate one and have Cyclic Prefix (CP) and the cycle is the targeting sequencing of the orthogonal sequence S (t) of T;

In first sequence emission cycle, have first targeting sequencing and the S (t) of CP by first transmission antennas transmit, have second targeting sequencing of CP and S (t-T/2) by second transmission antennas transmit; With

Second sequence emission cycle, by first transmission antennas transmit, first targeting sequencing, by second transmission antennas transmit, second targeting sequencing.

11, a kind of in adopting the orthogonal FDM communication system of four transmitting antennas the leading method of emission, comprise the following steps:

Generate one and have Cyclic Prefix (CP) and the cycle is the targeting sequencing of the orthogonal sequence S (t) of T;

In first sequence emission cycle, first targeting sequencing that has CP and S (t) by first transmission antennas transmit, second targeting sequencing that has CP and S (t-T/4) by second transmission antennas transmit, have the 3rd targeting sequencing of CP and S (t-T/2) by the 3rd transmission antennas transmit, have the 4th targeting sequencing of CP and S (t-3T/4) by the 4th transmission antennas transmit; With

Second sequence emission cycle, respectively by first to the 4th transmission antennas transmit, first to the 4th targeting sequencing.

12, a kind of in adopting the orthogonal FDM communication system of six transmitting antennas the leading method of emission, comprise the following steps:

Generate one and have Cyclic Prefix (CP) and the cycle is the targeting sequencing of the orthogonal sequence S (t) of T;

In first sequence emission cycle, first targeting sequencing that has CP and S (t) by first transmission antennas transmit, second targeting sequencing that has CP and S (t-T/4) by second transmission antennas transmit, the 3rd targeting sequencing that has CP and S (t-T/2) by the 3rd transmission antennas transmit, the 4th targeting sequencing that has CP and S (t-3T/4) by the 4th transmission antennas transmit, by the 5th transmission antennas transmit first targeting sequencing, by the 6th transmission antennas transmit second targeting sequencing; With

In second sequence emission cycle, by first transmission antennas transmit, first targeting sequencing, by second transmission antennas transmit, second targeting sequencing, by the 3rd transmission antennas transmit the 3rd targeting sequencing, by the 4th transmission antennas transmit the 4th targeting sequencing, by the 5th transmission antennas transmit have CP and-the 5th targeting sequencing of S (t), by the 6th transmission antennas transmit have CP and-the 6th targeting sequencing of S (t-T/4).

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